[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:07.03,0:00:09.40,Default,,0000,0000,0000,,Most atoms don't ride solo,
Dialogue: 0,0:00:09.40,0:00:12.12,Default,,0000,0000,0000,,instead they bond with other atoms.
Dialogue: 0,0:00:12.12,0:00:13.74,Default,,0000,0000,0000,,And bonds can form between atoms
Dialogue: 0,0:00:13.74,0:00:14.94,Default,,0000,0000,0000,,of the same element
Dialogue: 0,0:00:14.94,0:00:17.06,Default,,0000,0000,0000,,or atoms of different elements.
Dialogue: 0,0:00:17.06,0:00:20.19,Default,,0000,0000,0000,,You've probably imagined bonding as a tug of war.
Dialogue: 0,0:00:20.19,0:00:21.97,Default,,0000,0000,0000,,If one atom is really strong,
Dialogue: 0,0:00:21.97,0:00:24.11,Default,,0000,0000,0000,,it can pull one or more electrons
Dialogue: 0,0:00:24.11,0:00:25.78,Default,,0000,0000,0000,,off another atom.
Dialogue: 0,0:00:25.78,0:00:28.80,Default,,0000,0000,0000,,Then you end up with one negatively charged ion
Dialogue: 0,0:00:28.80,0:00:31.04,Default,,0000,0000,0000,,and one positively charged ion.
Dialogue: 0,0:00:31.04,0:00:33.81,Default,,0000,0000,0000,,And the attraction between these opposite charges
Dialogue: 0,0:00:33.81,0:00:35.98,Default,,0000,0000,0000,,is called an ionic bond.
Dialogue: 0,0:00:35.98,0:00:37.23,Default,,0000,0000,0000,,This is the kind of sharing
Dialogue: 0,0:00:37.23,0:00:39.99,Default,,0000,0000,0000,,where you just give away your toy to someone else
Dialogue: 0,0:00:39.99,0:00:41.96,Default,,0000,0000,0000,,and then never get it back.
Dialogue: 0,0:00:43.32,0:00:45.00,Default,,0000,0000,0000,,Table salt, sodium chloride,
Dialogue: 0,0:00:45.00,0:00:47.76,Default,,0000,0000,0000,,is held together by ionic bonds.
Dialogue: 0,0:00:47.76,0:00:50.33,Default,,0000,0000,0000,,Every atom of sodium gives up one electron
Dialogue: 0,0:00:50.33,0:00:52.25,Default,,0000,0000,0000,,to every atom of chlorine,
Dialogue: 0,0:00:52.25,0:00:53.36,Default,,0000,0000,0000,,ions are formed,
Dialogue: 0,0:00:53.36,0:00:55.24,Default,,0000,0000,0000,,and those ions arrange themselves
Dialogue: 0,0:00:55.24,0:00:57.91,Default,,0000,0000,0000,,in a 3D grid called a lattice,
Dialogue: 0,0:00:57.91,0:00:59.44,Default,,0000,0000,0000,,in which every sodium ion
Dialogue: 0,0:00:59.44,0:01:01.67,Default,,0000,0000,0000,,is bonded to six chloride ions,
Dialogue: 0,0:01:01.67,0:01:03.50,Default,,0000,0000,0000,,and every chloride ion is bonded
Dialogue: 0,0:01:03.50,0:01:05.71,Default,,0000,0000,0000,,to six sodium ions.
Dialogue: 0,0:01:05.71,0:01:07.47,Default,,0000,0000,0000,,The chlorine atoms never give
Dialogue: 0,0:01:07.47,0:01:09.92,Default,,0000,0000,0000,,the sodium atoms their electrons back.
Dialogue: 0,0:01:10.58,0:01:13.68,Default,,0000,0000,0000,,Now, these transactions aren't always so cut-and-dried.
Dialogue: 0,0:01:13.68,0:01:16.62,Default,,0000,0000,0000,,If one atom doesn't completely overwhelm the other,
Dialogue: 0,0:01:16.62,0:01:19.32,Default,,0000,0000,0000,,they can actually share each other's electrons.
Dialogue: 0,0:01:19.32,0:01:20.82,Default,,0000,0000,0000,,This is like a pot luck
Dialogue: 0,0:01:20.82,0:01:22.92,Default,,0000,0000,0000,,where you and a friend each bring a dish
Dialogue: 0,0:01:22.92,0:01:25.92,Default,,0000,0000,0000,,and then both of you share both dishes.
Dialogue: 0,0:01:25.92,0:01:27.35,Default,,0000,0000,0000,,Each atom is attracted to the shared electrons
Dialogue: 0,0:01:27.35,0:01:28.65,Default,,0000,0000,0000,,in between them,
Dialogue: 0,0:01:28.65,0:01:31.73,Default,,0000,0000,0000,,and this attraction is called a covalent bond.
Dialogue: 0,0:01:31.73,0:01:33.76,Default,,0000,0000,0000,,The proteins and DNA in our bodies,
Dialogue: 0,0:01:33.76,0:01:34.58,Default,,0000,0000,0000,,for example,
Dialogue: 0,0:01:34.58,0:01:37.78,Default,,0000,0000,0000,,are held together largely by these covalent bonds.
Dialogue: 0,0:01:37.78,0:01:39.36,Default,,0000,0000,0000,,Some atoms can covalently bond
Dialogue: 0,0:01:39.36,0:01:41.25,Default,,0000,0000,0000,,with just one other atom,
Dialogue: 0,0:01:41.25,0:01:42.92,Default,,0000,0000,0000,,others with many more.
Dialogue: 0,0:01:42.92,0:01:44.37,Default,,0000,0000,0000,,The number of other atoms
Dialogue: 0,0:01:44.37,0:01:45.69,Default,,0000,0000,0000,,one atom can bond with
Dialogue: 0,0:01:45.69,0:01:48.58,Default,,0000,0000,0000,,depends on how its electrons are arranged.
Dialogue: 0,0:01:48.58,0:01:51.54,Default,,0000,0000,0000,,So, how are electrons arranged?
Dialogue: 0,0:01:51.54,0:01:53.97,Default,,0000,0000,0000,,Every atom of a pure, unbonded element
Dialogue: 0,0:01:53.97,0:01:55.39,Default,,0000,0000,0000,,is electrically neutral
Dialogue: 0,0:01:55.39,0:01:56.83,Default,,0000,0000,0000,,because it contains the same number
Dialogue: 0,0:01:56.83,0:01:58.46,Default,,0000,0000,0000,,of protons in the nucleus
Dialogue: 0,0:01:58.46,0:02:01.25,Default,,0000,0000,0000,,as it does electrons around the nucleus.
Dialogue: 0,0:02:01.25,0:02:04.42,Default,,0000,0000,0000,,And not all of those electrons are available for bonding.
Dialogue: 0,0:02:04.42,0:02:06.42,Default,,0000,0000,0000,,Only the outermost electrons,
Dialogue: 0,0:02:06.42,0:02:08.68,Default,,0000,0000,0000,,the ones in orbitals furthest from the nucleus,
Dialogue: 0,0:02:08.68,0:02:10.34,Default,,0000,0000,0000,,the ones with the most energy,
Dialogue: 0,0:02:10.34,0:02:12.73,Default,,0000,0000,0000,,only those participate in bonding.
Dialogue: 0,0:02:12.73,0:02:15.81,Default,,0000,0000,0000,,By the way, this applies to ionic bonding too.
Dialogue: 0,0:02:15.81,0:02:17.49,Default,,0000,0000,0000,,Remember sodium chloride?
Dialogue: 0,0:02:17.49,0:02:19.40,Default,,0000,0000,0000,,Well, the electron that sodium loses
Dialogue: 0,0:02:19.40,0:02:21.60,Default,,0000,0000,0000,,is the one furthest from its nucleus,
Dialogue: 0,0:02:21.60,0:02:23.41,Default,,0000,0000,0000,,and the orbital that electron occupies
Dialogue: 0,0:02:23.41,0:02:25.03,Default,,0000,0000,0000,,when it goes over to chlorine
Dialogue: 0,0:02:25.03,0:02:28.28,Default,,0000,0000,0000,,is also the one furthest from its nucleus.
Dialogue: 0,0:02:28.28,0:02:30.17,Default,,0000,0000,0000,,But back to covalent bonding.
Dialogue: 0,0:02:30.17,0:02:31.69,Default,,0000,0000,0000,,Carbon has four electrons
Dialogue: 0,0:02:31.69,0:02:32.80,Default,,0000,0000,0000,,that are free to bond,
Dialogue: 0,0:02:32.80,0:02:34.13,Default,,0000,0000,0000,,nitrogen has three,
Dialogue: 0,0:02:34.13,0:02:35.41,Default,,0000,0000,0000,,oxygen two.
Dialogue: 0,0:02:35.41,0:02:37.27,Default,,0000,0000,0000,,So, carbon is likely to form four bonds,
Dialogue: 0,0:02:37.27,0:02:38.11,Default,,0000,0000,0000,,nitrogen three,
Dialogue: 0,0:02:38.11,0:02:39.60,Default,,0000,0000,0000,,and oxygen two.
Dialogue: 0,0:02:39.60,0:02:41.30,Default,,0000,0000,0000,,Hydrogen only has one electron,
Dialogue: 0,0:02:41.30,0:02:43.41,Default,,0000,0000,0000,,so it can only form one bond.
Dialogue: 0,0:02:43.41,0:02:44.89,Default,,0000,0000,0000,,In some special cases,
Dialogue: 0,0:02:44.89,0:02:46.43,Default,,0000,0000,0000,,atoms can form more bonds
Dialogue: 0,0:02:46.43,0:02:47.52,Default,,0000,0000,0000,,than you'd expect,
Dialogue: 0,0:02:47.52,0:02:49.100,Default,,0000,0000,0000,,but they better have a really good reason to do so,
Dialogue: 0,0:02:49.100,0:02:52.08,Default,,0000,0000,0000,,or things tend to fly apart.
Dialogue: 0,0:02:52.08,0:02:53.10,Default,,0000,0000,0000,,Groups of atoms
Dialogue: 0,0:02:53.10,0:02:55.11,Default,,0000,0000,0000,,that share electrons covalently with each other
Dialogue: 0,0:02:55.11,0:02:56.82,Default,,0000,0000,0000,,are called molecules.
Dialogue: 0,0:02:57.56,0:02:58.58,Default,,0000,0000,0000,,They can be small.
Dialogue: 0,0:02:58.58,0:03:00.61,Default,,0000,0000,0000,,For example, every molecule of oxygen gas
Dialogue: 0,0:03:00.61,0:03:03.09,Default,,0000,0000,0000,,is made up of just two oxygen atoms
Dialogue: 0,0:03:03.09,0:03:04.52,Default,,0000,0000,0000,,bonded to each other.
Dialogue: 0,0:03:04.52,0:03:06.19,Default,,0000,0000,0000,,Or they could be really, really big.
Dialogue: 0,0:03:06.19,0:03:09.38,Default,,0000,0000,0000,,Human chromosome 13 is just two molecules,
Dialogue: 0,0:03:09.38,0:03:13.02,Default,,0000,0000,0000,,but each one has over 37 billion atoms.
Dialogue: 0,0:03:13.02,0:03:14.21,Default,,0000,0000,0000,,And this neighborhood,
Dialogue: 0,0:03:14.21,0:03:15.18,Default,,0000,0000,0000,,this city of atoms,
Dialogue: 0,0:03:15.18,0:03:18.23,Default,,0000,0000,0000,,is held together by the humble chemical bond.